Methods and apparatus for finishing edges of glass sheets

ABSTRACT

A method for finishing an edge of a glass sheet comprises grinding the edge of the glass sheet with a grinding wheel. The glass sheet includes a first major surface, a second major surface substantially parallel to the first major surface, and the edge connecting the first and second major surfaces. The grinding produces a central edge portion and two chamfered edge portions connecting the central edge portion with the first and second major surfaces, respectively. The method further comprises polishing the central edge portion with at least one cup wheel rotated about a first axis substantially parallel with the first and second major surfaces of the glass sheet to polish the central edge portion, wherein an abrasive layer of the cup wheel comprises at least one of ferric oxide (Fe 2 O 3 ), silicon carbide (SiC), and ceric oxide (CeO 2 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of U.S. Provisional Application Ser. No. 62/449,806 filed on Jan. 24, 2017 the contents of which are relied upon and incorporated herein by reference in their entirety as if fully set forth below.

BACKGROUND

The disclosure relates to finishing of glass sheets, and more particularly to methods and apparatus for finishing, i.e., grinding, polishing, etc., the edges of glass sheets.

Liquid crystal displays (LCDs) are used widely as display devices for consumer electronics, e.g., televisions, mobile phones, handheld devices, etc., for the advantages such as compactness and outstanding performance in terms of high display resolution. In LCDs, backlight modules are used as the illumination scheme. That is, the LCDs are illuminated by a light source placed at the back or side of the display panel.

Inside back light modules, light guide plates (LGPs) are used to distribute and direct one-dimensional light sources into two-dimension uniform light while requiring a very limited space. The requirements for a high quality LGP are high transmittance of light and with little or no color shift among others. LGPs can be made of plastics or glasses. Among these two common materials, glasses are advantageous for its characteristics such as rigidity and lower thermal expansion.

However, for glass sheets used as LGPs of specifically edge-lit LCDs, the roughness level of the edges of the glass sheets after traditional edge finishing procedure (i.e., grinding and polishing of the edges), as well as the perpendicularity of the edges, is yet to be optimized. These non-optimized edge properties of the glass sheets affect the transmittance of light for the glass sheets. When such glass sheets having non-optimized edge properties are utilized as LGPs for edge-lit LCD panels, viewers of the LCD panels may observe irregular and/or uneven patterns (such as dots, lines, stripes, or random areas) under certain conditions. This phenomenon of non-uniformity in illuminance or brightness of LCD panels is referred to as Mura defects.

In order to reduce or eliminate the Mura defects resulted in the manufactured LCD panels, there is a need for methods and apparatus for further improving the process of grinding and polishing glass sheets and to provide improved roughness and perpendicularity of the edges of the glass sheet.

SUMMARY

In general, the present disclosure includes edge finishing apparatuses and related methods for finishing edges of glass sheets. The edge finishing apparatus comprises a grinding wheel and at least one polishing wheel, for example a cup wheel, the rotational axis of which is substantially parallel with the major surfaces of the glass sheet under processing. The abrasive surface (or abrasive layer) of a cup wheel is disposed on the rim of the cup wheel. This type of wheel exhibits a more uniform wear rate over the entire abrasive surface when compared to a grinding wheel that comprises an abrasive surface on the circumference thereof. The composition of the polishing cup wheels disclosed herein are also specially configured for improved polishing efficiency. In addition, the disclosed apparatus and methods may help achieve a reduction of down time and cost. During manufacturing of glass sheets, normally a process for inspection of the edge attributes is performed after the edge finishing procedure. The utilization of one or more cup wheels for polishing can help ensure stable edge quality of manufactured glass sheets, and the process for inspection may be omitted or performed on samples only.

Accordingly, a method for finishing an edge of a glass sheet is disclosed, comprising grinding the edge of the glass sheet with a grinding wheel, the glass sheet including a first major surface, a second major surface substantially parallel with the first major surface, and the edge connecting the first and second major surfaces, the grinding producing a central edge portion and two chamfered edge portions connecting the central edge portion with the first and second major surfaces, respectively. The method further comprises polishing the central edge portion with a first cup wheel rotated about a first axis substantially parallel with the first and second major surfaces of the glass sheet to polish the central edge portion, wherein an abrasive layer of the first cup wheel comprises at least one of Fe₂O₃, SiC, and CeO₂. The abrasive layer may comprise about 5% to about 15% of Fe₂O₃ by volume. The abrasive layer may comprise about 15% to about 27% of SiC or CeO₂ by volume. The abrasive layer may further comprise diamond particles comprising a particle size from about 2 micrometers to about 4 micrometers.

In embodiments, the method further comprising conveying at least one of the grinding wheel and the glass sheet such that a relative speed between the grinding wheel and the glass sheet is in a range from about 2 meters per minute to about 6 meters per minute. In some embodiments, the method may comprise conveying at least one of the first cup wheel and the glass sheet such that a relative speed between the first cup wheel and the glass sheet is in a range from about 4 meters per minute to about 10 meters per minute. The conveying is performed in a direction along a length of the edge of the glass sheet.

An average roughness Ra of the polished central edge portion is equal to or less than about 0.05 micrometers and a surface of the polished central edge portion can be within 0.1 degrees of perpendicularity relative to the first or second major surface. A transmittance of light through the polished central edge portion is equal to or larger than about 98% over a wavelength range from about 380 nm to about 750 nm, for example over a distance of about 500 mm.

The method may further comprise performing an intermediate polishing step on the central edge portion with a second cup wheel after grinding the edge of the glass sheet, but before polishing with the first cup wheel, wherein the second cup wheel is rotated about a second axis substantially parallel with the first and second major surfaces, and wherein grits of the second cup wheel are larger than grits of the first cup wheel. The method may include conveying at least one of the second cup wheel and the glass sheet such that a relative speed between the second cup wheel and the glass sheet is in a range from about 4 meters per minute to about 10 meters per minute. In some embodiments, the second cup wheel can comprise a plurality of slots distributed along an inner periphery of an abrasive surface of the second cup wheel.

In another embodiment, an apparatus for finishing an edge of a glass sheet is described, comprising a grinding wheel for grinding the edge of the glass sheet, the glass sheet comprising a first major surface, a second major surface substantially parallel with the first major surface and the edge connecting the first and second major surfaces, the grinding wheel further comprising a circumferential groove with a profile configured to form a central edge portion substantially perpendicular to the first and second major surfaces and two chamfered edge portions connecting the central edge portion to the first and second major surfaces. The apparatus further comprises a first cup wheel for polishing the central edge portion, the first cup wheel rotatable about a first axis substantially parallel with the first major surface and the second major surface, the first cup wheel comprising an abrasive layer comprising at least one of Fe₂O₃, SiC, and CeO₂.

In some embodiments, the abrasive layer can comprise about 5% to about 15% of Fe₂O₃ by volume. In some embodiments, the abrasive layer can comprise about 15% to about 27% of SiC or CeO₂ by volume. The first cup wheel comprises grits equal to or greater than about 5000 mesh (5000#).

In some embodiments, the apparatus may further comprise a second cup wheel configured to polish the central edge portion, the second cup wheel supported and rotatable about a second axis substantially parallel with the first major surface and the second major surface, wherein grits of the first cup wheel are smaller than grits of the second cup wheel. The second cup wheel may comprise a plurality of slots distributed along an inner periphery of an abrasive surface of the second cup wheel.

The apparatus may further comprise at least one conveyor coupled to either one of the first cup wheel and the glass sheet and configured to convey at least one of the first cup wheel and the glass sheet in a direction along a length of the edge of the glass sheet by a relative speed in a range from about 4 meters per minute to about 10 meters per minute.

In still another embodiment, a glass sheet is described comprising an edge finished by the apparatus described above, wherein a surface roughness of the central edge portion is less than about 0.05 micrometers.

Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments as described herein, including the detailed description which follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understanding the nature and character of the claims. The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the description serve to explain principles and operation of the various embodiments. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram of an exemplary process for finishing edges of glass sheets according to embodiments of the present disclosure;

FIG. 2A is a top view of an exemplary glass sheet;

FIG. 2B is a side view of the glass sheet of FIG. 2A;

FIG. 2C is a perspective view of the glass sheet of FIG. 2A;

FIG. 3A is a side view of an exemplary grinding wheel for finishing glass sheets, according to an embodiment of the present disclosure;

FIG. 3B is a side (edge) view of the glass sheet of FIG. 2A after processing by the grinding wheel of FIG. 3A;

FIG. 3C is a partial enlarged view of the glass sheet of FIG. 3B;

FIG. 4A is a cross sectional view of a cup wheel of an edge finishing apparatus according to some embodiments of the present disclosure;

FIG. 4B schematically illustrates the cup wheel of FIG. 4A processing a glass sheet;

and

FIG. 5 is a perspective view of an alternative cup wheel of the edge finishing apparatus according to further embodiments of the present disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to the various embodiments, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts.

This description will be directed in particular to embodiments forming part of, or cooperating more directly with, an apparatus in accordance with the present disclosure. It is to be understood that embodiments not specifically shown or described may take various forms. Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

As used herein, grit size is designated by the word “mesh” following the git size, or, alternatively, “#”. According, a grit size of 5000 mesh may also be designated by 5000#.

The following descriptions provide a general description regarding the glass sheets under processing (more specifically, edge finishing) by the apparatus and/or method of the present disclosure.

After a glass sheet is formed, for example by scoring or cutting a glass ribbon or another glass sheet, edge surfaces of the glass sheet may need further processing to achieve a desired edge finish. Accordingly, FIG. 1 schematically illustrates a method 100 for processing an edge of a glass sheet. In accordance with FIG. 1, in a first step 102 the edge of the glass sheet is ground using a grinding wheel. In one or more following steps, polishing is performed by one or more polishing wheels. For example, in an optional coarse polishing step 104, the ground edge of the glass sheet may be polished with a first, coarse polishing wheel. Alternatively, in some embodiments, polishing may proceed directly from grinding to a fine polishing step 106 without the need for coarse polishing step 104. Both coarse and fine polishing may be performed using cup wheels, as described herein below in more detail.

FIGS. 1A-1C are schematic views of a glass sheet 200 as described herein. The glass sheet 200 comprises a first major surface 202, a second major surface 204 substantially parallel with the first major surface 202, and edge surfaces (or simply “edges”) 206 and 208 connecting the first and second major surfaces 202, 204. The distance between the first and second major surfaces 202, 204, which is also the height of the edge surfaces 206 and 208, defines a thickness T of the glass sheet 200. During manufacturing processes, glass sheet 200 may be conveyed in a conveyance direction 210. Although the edge surfaces 206 and 208 are shown as planar surfaces in FIGS. 1A-1C, it should be noted that edge surfaces 206 and 208 may in further embodiments comprise other shapes. For example, in some embodiments, edge surface 206 and/or edge surface 208 may comprise a chamfered surface or a rounded surface, for example as a result of a previous grinding and/or polishing operation.

In various embodiments of the present disclosure, the thickness of glass sheet 200 can be in a range from about 100 μm to about 3 mm, from about 300 μm to about 3 mm, from about 400 μm to about 2 mm, from about 0.5 mm to about 1 mm, or from about 0.5 mm to about 0.7 mm, including all ranges and sub-ranges therebetween, without departing from the scope of the disclosure.

Glass sheet 200 may be positioned with first and second major surfaces 202, 204 parallel with a horizontal plane. It should be appreciated, however, that such an orientation is not a requirement for any embodiment of the present disclosure, and the scope of the subject matter is not limited as such. Accordingly, glass sheet 200 may be oriented in other planes, such as a vertical plane, or any other plane between horizontal and vertical.

In FIGS. 2A-2C, glass sheet 200 may be conveyed in conveyance direction 210 by any suitable conveyor (not shown). It should be appreciated that in accordance with the foregoing, glass sheet 200 can be placed in different orientations, and conveyance direction 210 may vary based on the needs of different processes. It should also be appreciated that in further embodiments, glass sheet 200 may be fixed in a position. Further, although the embodiments described herein are directed to a glass sheet with rectangular shape, it should be appreciated that the glass sheet may be processed while in many different shapes.

Embodiments of the present disclosure include an edge finishing apparatus for processing one or more edges of a glass sheet, the edge finishing apparatus comprising a grinding wheel 300 for grinding the edges of the glass sheet 200. FIG. 3A schematically illustrates an exemplary grinding wheel 300 and a portion of glass sheet 200.

Grinding wheel 300 comprises a circumferential groove 302 located at the periphery of the grinding wheel, circumferential groove 302 comprising an abrasive surface. Circumferential groove 302 may have a profile configured to shape an edge of the glass sheet into any desired edge profile. For example, in some embodiments, circumferential groove 302 can comprise two transition sections 304 and 306 and a middle section 308, the transition sections configured to produced chamfered surfaces on the edge of glass sheet 200, e.g., edge 206.

Grinding wheel 300 is rotated about a central rotational axis 310 at a predetermined rotational speed during grinding. The rotational speed may be at least 3,600 revolutions per minute (rpm) so as to efficiently grind an edge surface, e.g., edge surface 206, of the glass sheet 200, for example in a range from about 3,600 rpm to about 6,000 rpm. The grinding wheel 300 may be supported and rotated by a spindle coupled to a motor. Either clockwise or counterclockwise rotation directions may be employed.

Grinding wheel 300 may be positioned such that rotational axis 310 is substantially parallel with a normal to the first and second major surfaces 202 and 204 of glass sheet 200. Moreover, grinding wheel 300 and glass sheet 200 can be aligned in respect of each other such that a mid-plane bisecting edge 206 along a direction parallel with the first and second major surfaces 202, 204 extends through the midpoint of the middle section 308 of grinding wheel 300.

In some embodiments, glass sheet 200 may be conveyed in conveyance direction 210 by any suitable conveyor (not shown) in a direction along a length of the edge surface 206 (i.e., outward from the page as in FIG. 3A) during grinding and grinding wheel 300 of the edge finishing apparatus may be fixed at a position adjacent the conveyance path of the glass sheet 200. In other embodiments, grinding wheel 300 can be moved by another conveyer (not shown) along the length of an edge of glass sheet 200 (such as the edge surface 206) while the glass sheet 200 is in a fixed position. In further embodiments, both glass sheet 200 and grinding wheel 300 may move in opposite directions along the length of the edge surface 206. A relative speed between grinding wheel 300 and glass sheet 200 can be in a range from about 2 meters per minute to about 6 meters per minute.

As edge surface 206 of glass sheet 200 is ground by grinding wheel 300, different sections 304, 306, and 308 of circumferential groove 302 can shape edge surface 206 into a central edge portion 212 substantially perpendicular to both the first and second major surfaces 202 and 204 and two chamfered edge portions 214 and 216, as schematically illustrated in FIG. 3B (not shown to scale).

The two chamfered edge portions 214 and 216 connect central edge portion 212 with first major surface 202 and second major surface 204, respectively. By chamfering the edges of glass sheet 200, fracturing or chipping of the glass sheet can be avoided, such as during subsequent handling, for example when transferring glass sheet 200 to a subsequent processing step or site, packaging, or shipping glass sheet 200.

As shown in FIG. 3B, chamfered edge portion 214 (216) comprises a chamfer height denoted as “C.” Preferably, chamfer height C of chamfered edge portions 214 and 216 are equal, although in further embodiments, the individual chamfer heights may be unequal. It will be appreciated that chamfer height C should be as small as possible, since it is central edge portion 212, rather than chamfered edge portions 314 and 316, that contributes to the overall optical quality of the glass sheet 200, particularly when used as an edge-lighted light guide plate in a back light unit. More specifically, it has been found that when central edge portion 212 comprises a large proportion of the thickness of glass sheet 200, better measurements of the transmittance of light for the edges of glass sheet 200 are obtained. In some embodiments, wherein thickness T of the glass sheet 200 is about 2.0 mm, chamfer height C obtained from the grinding process is less than 0.2 mm. In other embodiments, wherein thickness T of glass sheet 200 is about 0.7 mm, chamfer height C obtained from the grinding process is in a range of about 0.02 mm to about 0.08 mm.

After grinding by grinding wheel 300, the resultant central edge portion 212 may be substantially perpendicular to first major surface 202 and second major surface 204 of glass sheet 200, however central edge portion 212 may still exhibit a small deviation from perpendicularity. FIG. 3C is an enlarged and exaggerated view of part of central edge portion 212 after grinding. A line 312 perpendicular with first major surface 202 and second major surface 204 is shown for comparison. The surface of central edge portion 212 and line 312 form an angle 0. In embodiments of the present disclosure, angle 0 after grinding edge surface 206 with grinding wheel 300 may be in a range from about −2 to about +2 degrees.

Moreover, after grinding by grinding wheel 300, the roughness of the surface of central edge portion 212 may be greater than the roughness of edge surface 206 prior to grinding. As described herein, roughness is measured as an arithmetic average roughness (hereinafter “Ra”) of a surface. In embodiments of the present disclosure, the value of Ra for central edge portion 212 after grinding but prior to polishing can be about 0.5 μm. The roughness of the ground edge surface influences the transmittance of light, and the measured transmittance of light through the central edge portion 212 after grinding is only about 2%. Accordingly, glass sheet 200, when subjected only to grinding, may be unsuitable as a light guide plate in a back light unit, and in particular for a light guide plate intended to be lighted from an edge thereof.

Since grinding alone may not be sufficient for providing optimal edges of glass sheet 200, the edge finishing apparatus for processing glass sheets described herein may further comprise one or more polishing wheels for polishing the ground edge after grinding by the grinding wheel 300, for example one or more cup wheels. Accordingly, process 100 may include an optional intermediate polishing step 1004 and a fine polishing step 106.

FIG. 3A is a cross sectional view of an exemplary cup wheel 400 suitable for use with the edge finishing apparatus of the present disclosure. The sectional view of FIG. 3A is taken along the direction of a central rotational axis 402 of cup wheel 400, about which cup wheel 400 is rotated.

The cup wheel 400 comprises base portion 404 and ring portion 406 integrated to base portion 404. Base portion 404 may be a plate comprising a circular shape, and ring portion 406 may be integrated to base portion 404 about an outer periphery of base portion 404.

Ring portion 406 comprises a generally annular abrasive layer 408 concentric with rotational axis 402 and disposed over the surface of ring portion 406 opposing base portion 404. Abrasive layer 408 comprises abrasive grits for polishing, and may also further comprise other materials to enhance polishing effects. The surface of abrasive layer 408 is substantially flat.

In embodiments of the present disclosure, the thickness (height) of abrasive layer 408 may be in a range from about 2 mm to about 7 mm, for example about 5 mm, however the thickness of layer 204 is not limited as such, and may be other thicknesses .

Ring portion 406 is illustrated as a hollow cylinder in FIG. 4A. It should be appreciated that other shapes of ring portion 406 of cup wheel 400 are possible without departing from the scope of the present disclosure. For example, the outer diameter of ring portion 406 may be diverging or converging from one end to another.

In embodiments where ring portion 406 of cup wheel 400 comprises a hollow cylinder, width W of ring portion 406 (and also the width of annular abrasive layer 408) may, for example, be in a range from about 10 mm to about 20 mm, for example in a range from about 12 mm to about 15 mm, although other values for width W of ring portion 406 are also contemplated. However, width W of ring portion 406 (i.e., a width of a wall of the ring portion) is preferably greater than thickness T of glass sheet 200 to be polished, as will be explained below. In addition, width W of ring portion 406 should be large enough for ring portion 406 to be efficiently and stably mounted on base portion 404. FIG. 3B is a perspective view of cup wheel 400 of FIG. 3A shown engaged with glass sheet 200.

Cup wheel 400 is rotated about rotational axis 402 at a rotational speed during polishing in a range from about 3,600 rpm to about 6,000 rpm. Rotation may be performed in either a clockwise or counterclockwise rotation. Cup wheel 400 may be supported and rotated by a spindle coupled to a motor.

Cup wheel 400 may be positioned such that rotational axis 402 is parallel with first and second major surfaces 204, 206 of glass sheet 200 such that abrasive layer 408 contacts central edge portion 212 of glass sheet 200.

In some embodiments, glass sheet 200 is conveyed by a conveyor (not shown) in conveyance direction 210 along a length of the central edge portion 212 (i.e. outward from the page as in FIG. 4B) during polishing, and cup wheel 400 is fixed at a position aside the conveyance path of the glass sheet 200. In other embodiments, cup wheel 400 of the edge finishing apparatus may be moved by another conveyor (not shown) along the length of the edge surface of glass sheet 200 under processing (such as central edge portion 212) while glass sheet 200 is in a fixed position. In further embodiments, both glass sheet 200 and cup wheel 400 may be moved in opposite directions along the length of central edge portion 212 at a relative speed. In some embodiments, the relative speed between cup wheel 400 of the edge finishing apparatus and glass sheet 200 is in a range from about 4 meters per minute to about 10 meters per minute.

The type of wheels having the abrasive surface on the periphery of the wheel and being rotated about an axis substantially perpendicular to the major surfaces of the glass sheet, such as grinding wheel 300 illustrated in FIG. 3A, may have a smaller proportion of the abrasive surface worn faster than the rest of the abrasive surface, since each point along the edge of the glass sheet may only contact a corresponding periphery of the grinding wheel while being ground. On the other hand, cup wheels, such as cup wheel 400, may exhibit a slower wear rate of its abrasive surface, since the area of the abrasive surface contacted by the work piece (e.g. glass sheet 200) during polishing comprises a larger proportion of the abrasive surface. Moreover, because the rotational axis of the cup wheel is substantially parallel with glass sheet 200, wear of the cup wheel is uniformly distributed across the surface of abrasive layer 208 overall, and thus the lifespan of the cup wheel may be extended.

In some embodiments, the polishing cup wheel may comprise a slotted cup wheel, such as cup wheel 500 illustrated in FIG. 5. Slotted cup wheel 500 may, in some embodiments, be identical to cup wheel 400 with the exception that cup wheel 500 is formed with a plurality of slots 502 substantially radially and uniformly distributed across the whole outer surface of abrasive layer 508. In some embodiments, slots 502 are evenly distributed on an inner periphery of abrasive layer 508. In some embodiments, abrasive layer 508 may comprise from about 20 slots to about 30 slots. Slot widths may, in some embodiments, be from about 3 mm to about 4 mm. Slots may be arranged, for example at an angle in a range from about 40° to about 50° relative to a diameter of cup wheel 500.

Slots 502 can be effective for dissipating heat generated during polishing. Slots 502 can also provide slotted cup wheel 500 with more abrasion efficiency than cup wheel 200 illustrated in FIGS. 3A, 3B, since the slots can help remove more material of the glass sheet during polishing.

Although the slots 502 in FIG. 4 are illustrated as uniform stripe shapes, other shapes and arrangement of slots 502 may be employed.

In embodiments of the present disclosure, the composition of abrasive layers 408, 508 may comprise materials that enhance polishing. Table 1 lists exemplary ingredients of abrasive layers 408, 508 of cup wheels 400, 500 according to some embodiments.

TABLE 1 Ingredients Volume composition Epoxy 20% to 40% Cu 20% to 50% ZnO 25% to 30% MgO 1% to 3% Fe₂O₃  5% to 15% SiC or CeO₂ 15% to 27%

In embodiments of the present disclosure, abrasive layers 408, 508 of cup wheels 400, 500 can comprise ceric oxide (CeO₂), silicon carbide (SiC), and/or ferric oxide (Fe₂O₃) as polishing agents to improve polishing efficiency. In some embodiments, abrasive layers 408, 508 can comprise about 5% to 15% of Fe₂O₃ by volume. In some embodiments, abrasive layers 408, 508 can comprise at least one of CeO₂ and SiC in an amount in a range from about 15% to about 27% by volume.

Abrasive layers 408, 508 may also comprise copper (Cu) to facilitate heat dissipation, for example in a range from about 20% to 50% by volume, for example in a range from about 20% to about 50% by volume. For example, in some embodiments, a cup wheel designated for fine polishing (i.e., fine polishing step 106) may comprise Cu in an amount from about 40% to about 50% by volume, whereas a cup wheel designated for coarse grinding (i.e., coarse polishing step 104) may comprise Cu in an amount from about 20% to about 40%.

In some embodiments, cup wheels 400, 500 may include diamond particles, wherein an average particle size may range from about 2 micrometers to about 8 micrometers, for example in a range from about 2 micrometers to about 6 micrometers, for example in a range from about 2 micrometers to about 4 micrometers, for example in a range from about 6 micrometers to about 8 micrometers. Diamond particles may be in an amount in a range from about 0.5% by volume to about 1.5% by volume. Typically, a fine polishing cup wheel comprises diamond particles with an average particle size in a range from about 2 micrometers to about 4 micrometers, whereas a coarse polishing cup wheel comprises diamond particles with an average particle size in a range from about 6 micrometers to about 8 micrometers, although in further embodiments, other average particle sizes may be used.

In embodiments, cup wheels 400, 500 may be resin bonded wheels, and abrasive layers 408, 508 may comprise a resin bonding agent in an amount from about 20% by volume to about 40% by volume. The resin mixed with the abrasive materials is used as a bonding material for holding the abrasive materials together in place in the abrasive layer. Other bonding materials suitable for holding the abrasive materials described above may be contemplated. Typically, a fine polishing cup wheel comprises epoxy resin in an amount from about 30% to about 40% by volume, whereas a coarse polishing cup wheel may comprise epoxy resin in an amount from about 30% to about 30% by volume, although in further embodiments, different volumes of epoxy resin may be used.

As described supra, in some embodiments, edge processing method 100 includes grinding step 102 performed using grinding wheel 300 as previously described, followed by polishing. For example, edge processing method 100 may include grinding step 102 and fine polishing step with a fine polishing wheel, such as cup wheel 400. During grinding step 102, edge surface 206 of glass sheet 200 is ground with circumferential groove 302 of grinding wheel 300. Grinding wheel 300 is rotated about rotational axis 310 substantially parallel with a normal to first and second major surfaces 202 and 204. The grinding produces a central edge portion 212 and two chamfered edge portions 214, 216 connecting central edge portion 212 with first major surface 202 and second major surface 204. Central edge portion 212 is substantially perpendicular to both first and second major surfaces 202, 204.

To provide central edge portion 212 with improved perpendicularity and smoothness, in some embodiments a fine polishing step may be performed immediately after the grinding step using cup wheel 400 to produce a polished central edge portion 212. Cup wheel 400 is rotated about an axis substantially parallel with both first and second major surfaces 202, 204 of glass sheet 200.

In further embodiments, edge processing method 100 may also comprise an intermediate polishing step 104, for example with cup wheel 500, after grinding step 102 but before fine polishing step 106. Accordingly, during step 104, a second cup wheel may be used for coarse polishing the ground central edge portion 212, so as to produce a more smoothly-finished central edge portion. The coarse polishing cup wheel employed during step 104 comprises larger abrasive grits than the fine polishing cup wheel used during step 106. Both the coarse polishing cup wheel and the fine polishing cup wheel are rotated about axes of rotation substantially parallel with both the first and second major surfaces 202, 204 of glass sheet 200 during optional course polishing step 104 and fine polishing step 106.

The fine polishing wheel (e.g., cup wheel 400) differs from the coarse polishing wheel (e.g., cup wheel 500) in at least the sizes of the abrasive grits thereof. In other words, in embodiment wherein the edge finishing apparatus comprises two (or even more) cup wheels for polishing the edges of the glass sheet, the two cup wheels may have different sizes of the abrasive grits.

The size of the abrasive grits for abrasive wheels is typically measured in “mesh,” which means the number of apertures per square inch of sieving screen for the grits. In embodiments of the present disclosure, the grinding wheel (such as grinding wheel 300) of the edge finishing apparatus may be 800 mesh or 1200 mesh, and the cup wheels used during either the coarse polishing process or the fine polishing process are such as 2000 mesh, 3000 mesh, 5000 mesh, 6000 mesh, and 9000 mesh. Typically, the fine polishing cup wheel comprises a grit equal to or greater than about 5000 mesh, for example in a range from about 5000 mesh to about 9000 mesh, for example in a range from about 5000 mesh to about 8000 mesh, for example in a range from about 5000 mesh to about 7000 mesh, or in a range from about 5000 mesh to about 6000 mesh.

Additionally, cup wheel 500 tends to produce more aggressive polishing, removing more material than an un-slotted polishing wheel, and therefore cup wheel slotted cup wheel 500 is more desirable during intermediate polishing step 104.

It may be appreciated that steps 102, 104 and 106 may each be repeated multiple times, as needed.

It may also be appreciated that multiple grinding and/or polishing wheels may be in operation simultaneously in some implementations. For example, in some embodiments there may be two grinding wheels in the edge finishing apparatus, each simultaneously grinding opposing edges of a glass sheet.

EXAMPLES

The following Tables 2-6 disclose example configurations in different embodiments of the present disclosure. The measured average roughness Ra and the transmittance of light for the edge finished by the apparatus and/or method of the present disclosure are also disclosed. All roughness values were obtained using a Keyance VK-850 30 Laser Scanning Confocal Microscope.

Among these parameters, the values in the column “Type of Wheel” refer to the wheel that is used and the size of its abrasive grits (in mesh), wherein “G” indicates the type of wheel, “C” indicates a cup wheels such as cup wheel 400, and “S” indicates a slotted cup wheel such as cup wheel 500. The parameter “Conveyance Speed” refers to the relative speed between the glass sheet and the edge finishing apparatus. The parameter “removal amount” refers to the amount of the glass sheet removed by the respective grinding and/or polishing wheel of the edge finishing apparatus.

TABLE 2 Conveyance Removal Process Type of Speed Amount Repetition step Wheel (meter/minute) (mm) times Grinding G, 800# 6 0.1 1 Polishing C, 5000# 2 0.005 3 Ra 0.03 μm-0.05 μm Transmittance 98.5%-99.3% of Light

TABLE 3 Conveyance Removal Process Type of Speed Amount Repetition step Wheel (meter/minute) (mm) times Grinding G, 800# 6 0.1 1 Fine C, 6000# 6 0.005 3 Polishing Ra 0.03 μm-0.04 μm Transmittance 98.9% of Light

TABLE 4 Conveyance Removal Process Type of Speed Amount Repetition step Wheel (meter/minute) (mm) times Grinding G, 800# 2 0.1 1 Fine C, 9000# 2 0.005 4 Polishing Ra 0.03 μm-0.04 μm Transmittance 98.9% of Light

TABLE 5 Conveyance Removal Process Type of Speed Amount Repetition step Wheel (meter/minute) (mm) times Grinding G, 800# 6 0.1 1 Coarse Polishing S, 2000# 6 0.01 1 Fine Polishing C, 9000# 6 0.005 1 Ra 0.04 μm-0.05 μm Transmittance 99.26% of Light

According to the examples described in the present disclosure, the arithmetic average roughness (Ra) of the edge surface (such as the central edge portion 212 in FIG. 3B) after being ground by grinding wheel 300 is about 0.5 μm. The finished edge surface, e.g., the central edge portion 212 after being processed by the edge finishing apparatus (e.g., after polishing with fine polishing step 106 and optionally intermediate polishing step 104), comprises a value of Ra equal to or less than about 0.05 μm.

Moreover, the finished edge surface may be substantially perpendicular to the major surfaces of the glass sheets with only a 0.1 degree deviation. That is, the value of the angle θ as indicated in FIG. 3C for the central edge portion 212 after being processed by the edge finishing apparatus is in the range of −0.1 to 0.1 degree. As the roughness level is improved, the transmittance of light for the edges finished by the edge finishing apparatus and method hereof may achieve 98% and above.

The improved transmittance of light for the edges achieved by adopting the embodiments discussed in this disclosure in turn can reduce the occurrence of variations in luminance of a display panel, known as Mura defects.

It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the subject matter. 

1. A method for finishing an edge of a glass sheet, comprising: grinding the edge of the glass sheet with a grinding wheel, the glass sheet including a first major surface, a second major surface substantially parallel with the first major surface, and the edge connecting the first and second major surfaces, the grinding producing a central edge portion and two chamfered edge portions connecting the central edge portion with the first and second major surfaces, respectively; and polishing the central edge portion with a first cup wheel rotated about a first axis substantially parallel with the first and second major surfaces of the glass sheet to polish the central edge portion, wherein an abrasive layer of the first cup wheel comprises at least one of Fe₂O₃, SiC, and CeO₂.
 2. The method of claim 1, wherein the abrasive layer comprises about 5% to about 15% of Fe₂O₃ by volume.
 3. The method of claim 1, wherein the abrasive layer comprises about 15% to about 27% of SiC or CeO₂ by volume.
 4. The method of claim 1, wherein the abrasive layer further comprises diamond particles comprising a particle size from about 2 micrometers to about 4 micrometers.
 5. The method of claim 1, further comprising conveying at least one of the grinding wheel and the glass sheet such that a relative speed between the grinding wheel and the glass sheet is in a range from about 2 meters per minute to about 6 meters per minute.
 6. The method of claim 1, further comprising conveying at least one of the first cup wheel and the glass sheet such that a relative speed between the first cup wheel and the glass sheet is in a range from about 4 meters per minute to about 10 meters per minute.
 7. (canceled)
 8. The method of claim 1, wherein an average roughness Ra of the polished central edge portion is equal to or less than about 0.05 micrometers.
 9. The method of claim 1, wherein a surface of the polished central edge portion is within 0.1 degrees of perpendicularity relative to the first or second major surface.
 10. The method of claim 1, wherein a transmittance of light of the polished central edge portion is equal to or larger than about 98% over a wavelength range from about 380 nm to about 750 nm.
 11. The method of claim 1, further comprising performing intermediate polishing on the central edge portion with a second cup wheel after grinding the edge of the glass sheet, wherein the second cup wheel is rotated about a second axis substantially parallel with the first and second major surfaces, and wherein grits of the second cup wheel are larger than grits of the first cup wheel.
 12. The method of claim 11, further comprising conveying at least one of the second cup wheel and the glass sheet such that a relative speed between the second cup wheel and the glass sheet is in a range from about 4 meters per minute to about 10 meters per minute.
 13. The method of claim 11, wherein the second cup wheel comprises a plurality of slots distributed along an inner periphery of an abrasive surface of the second cup wheel.
 14. An apparatus for finishing an edge of a glass sheet, comprising: a grinding wheel for grinding the edge of the glass sheet, the glass sheet comprising a first major surface, a second major surface substantially parallel with the first major surface and the edge connecting the first and second major surfaces, the grinding wheel further comprising a circumferential groove with a profile configured to form a central edge portion substantially perpendicular to the first and second major surfaces and two chamfered edge portions connecting the central edge portion to the first and second major surfaces; and a cup wheel for polishing the central edge portion, the cup wheel rotatable about a first axis substantially parallel with the first major surface and the second major surface, the cup wheel comprising an abrasive layer comprising at least one of Fe₂O₃, SiC, and CeO₂.
 15. The apparatus of claim 14, wherein the abrasive layer comprises about 5% to about 15% of Fe₂O₃ by volume.
 16. The apparatus of claim 14, wherein the abrasive layer comprises about 15% to about 27% of SiC or CeO₂ by volume.
 17. The apparatus of claim 14, further comprising a second cup wheel configured to polish the central edge portion, the second cup wheel supported and rotatable about a second axis substantially parallel with the first major surface and the second major surface, wherein grits of the first cup wheel are smaller than grits of the second cup wheel.
 18. The apparatus according to claim 17, wherein the second cup wheel comprises a plurality of slots distributed along an inner periphery of an abrasive surface of the second cup wheel.
 19. The apparatus according to claim 17, wherein the first cup wheel comprises 5000 mesh grits.
 20. The apparatus of claim 14, further comprising at least one conveyor coupled to either one of the first cup wheel and the glass sheet and configured to convey at least one of the first cup wheel and the glass sheet in a direction along a length of the edge of the glass sheet by a relative speed in a range from about 4 meters per minute to about 10 meters per minute.
 21. (canceled) 